A power supply capable of generating a specified DC voltage from an AC power supply is a known prior art. The power supply is generally provided with a smoothing circuit having a large-capacity capacitor after a rectifying device.
A large current instantaneously passes through a large-capacity capacitor by accumulated power immediately after energization. The current may reach some tens through hundred amperes. If the instantaneous current is too large, the life of a power supply switch, a rectifying diode, etc. is affected badly.
To avoid the harmful effect, a rush current passing through the rectifying diode and the capacitor when the power supply switch is input is generally reduced by limiting the current of an output circuit by serially arranging current limiting resistors on the downstream of the power supply switch of the power supply.
However, since a current loss grows when a fixed resistance is used for current limiting, a power thermistor, which is a large NTC (negative temperature coefficient) thermistor with a low resistance, is generally used.
The thermistor normally has a room temperature resistance of several to 20Ω, and the resistance is reduced to about 1/10 after limiting the rush current. Therefore, the current limiting effect cannot sufficiently work if the power supply is powered up immediately after cutting off the power supply before the cooling time of the thermistor is not long enough with the resistance not reaching the room temperature resistance.
It is a hot start state, and the current exceeding the current limit value of the component configuring the electric circuit of a switch, a rectifying diode, a smoothing capacitor, etc. passes through the electric circuit energized in this state. Then, the short circuit of the rectifying diode, the short circuit of the smoothing capacitor, etc. occur, and damage the current limiting resistor by a fire, and may damage the switch.
To prevent the component in the electric circuit having the current limiting resistor from being damaged, there is, for example, the technology proposed for short-circuiting both ends of the current limiting resistor using a relay (for example, refer to patent document 1).
In another example, there is the technology of a power supply circuit proposed for suppressing a rush current of a switching power supply using a complicated circuit configuration (for example, refer to patent document 2).
In a further example, to prevent the damage by a fire of the current limiting resistor due to a rush current, there is the technology proposed by opening and closing a bimetal switch (for example, refer to patent document 3).
In a further example, to protect a lightning arrestor in an example of an electric circuit provided with the lightning arrestor, there is the proposed technology in which a resistor and a thermal fuse are serially connected to the lightning arrestor (for example, refer to patent document 4).
In another example of protecting a lightning arrestor, there is the technology for suppressing the abnormal heat generation by generating a gap in series with the lightning arrestor in an abnormal state (for example, refer to patent document 5).